HSPH scientists have found that women who follow a combination of at least five low-risk lifestyle factors, including diet, weight control, and physical activity, can decrease their risk of ovulatory-disorder infertility by 69 percent compared to women who follow between zero and four low-risk lifestyle factors.
The nutritionists first focused on polycystic ovary syndrome (PCOS), a condition that contributes to several disorders, including menstrual irregularity and infertility. PCOS appears to be linked to insulin resistance, which in turn can be influenced by diet.
“We wanted to know whether anything influencing insulin sensitivity, including diet, would also improve reproductive function in otherwise healthy women and not only women with PCOS,” said the study’s lead author, Jorge Chavarro, a research fellow in the Department of Nutrition at HSPH. Walter Willett, chair of the department and the Fredrick John Stare professor of epidemiology and nutrition, is the senior author.
For every six couples who try to get pregnant, one pair faces infertility; ovulatory disorders affect 18 to 30 percent of these couples. To identify a fertility diet, the HSPH researchers followed 17,544 women without a history of infertility who were trying to or became pregnant during the eight-year prospective study, which appears in the Nov. 1 issue of Obstetrics & Gynecology.
Women who had the highest fertility score consumed less trans fat, more vegetable protein, more carbohydrates with high fiber and a low glycemic index, more nonheme iron, more multivitamins, and more high-fat dairy products, among other choices.
The high-fat dairy product component may be surprising. Galactose studies in mice, for example, have linked the sugar to premature ovarian failure. And a 1994 study from Brigham and Women’s Hospital reported that ingesting galactose may negatively affect ovarian function.
Yet, said Chavarro, “we found that low-fat dairy products were, in fact, associated with a higher risk of infertility.” He is unsure why this is the case but speculated that bovine hormones may be present in higher quantities in high-fat milk and could facilitate women’s fertility.
In addition to diet, the study analyzed body mass index (BMI). The researchers graphed a U-shaped relationship between BMI and ovulatory- disorder infertility; women with a BMI between 20 and 25 had a lowered infertility risk while women with a BMI on either side of this range had a similar heightened risk of infertility.
Vigorous exercise—more than 30 minutes per day—had no effect on ovulatory disorders until the researchers removed BMI from the equation, showing that exercise led to a slightly lower risk for ovulatory infertility.
The study found that fertility rose for each additional low-risk lifestyle factor a woman followed. Women who abided by five or more factors experienced a sixfold decrease in risk compared to women who followed none.
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